New research has shown for the first time in mice that cardiac complications associated with the flu are not caused by lung inflammation, as predicted previously, according to Science Daily.

Instead, researchers at the Ohio State University revealed that influenza infection directly affects cardiac cells, causing electrical malfunctions and heart scarring in some patients with severe flu.

The researchers had seen flu viral particles in cardiac cells of infected mice in previous work. However, they could not say for sure their presence in the heart was driving cardiac damage.

When they infected mice with a genetically altered flu virus, which was not able to replicate in heart cells, the mice developed inflammatory flu symptoms but no cardiac complications.

Lead author Dr. Jacob Yount said, “We showed that even when you have a very severe infection in the lungs, if you’re using that virus that can’t replicate in the heart, you don’t get those cardiac complications.”

“It proves it’s direct infection of the heart that’s driving these complications,” he added. “Now we need to figure out what direct infection does: Is it killing heart cells? Does it have long-term ramifications? Do repeated infections have heart complications that build up over time? There are a lot of questions now for us to answer.”

There is growing evidence that some hospitalized flu patients can develop heart problems. One recent study found that about 12% of American adults hospitalized with the flu over eight years developed sudden, serious cardiac complications.

Dr. Yount explained, “We know those people are more susceptible to severe flu infections, and our mouse research would suggest they’re also more susceptible to heart complications with the flu.”

“We have this mouse model and this virus that allowed us to distinguish between the severe lung inflammation and the direct replication of the virus in the heart,” he explained. “We hadn’t been able to separate those two things in the past. If you don’t have the virus replicating strongly in the heart, you don’t see the same electrical abnormalities or the same fibrotic response.”

The researchers said there is still a lot to learn. The flu virus often infiltrates the lungs. It generally is not present in the blood or other organs; however, it does get to the heart.

Dr. Yount said the study findings, published Wednesday in the journal Science Advances, suggest clearing the viral infection could be key to reducing flu’s problematic effects on the heart. “One thing this tells us is that this is another reason to get your flu shot because you don’t want your heart to get infected by the flu — and it is a possibility,” he explained.